The present invention generally relates to the preparation of substituted 3-aryl-5-haloalkyl-pyrazoles having herbicidal activity, and specifically, to novel processes for preparing C.sub.1-5 alkyl esters of 5-[1-(C.sub.1-5 alkyl)-4-halo-5-(C.sub.1-3 haloalkyl)-1 H-pyrazole-3-yl]-2,4-dihalo-benzoic acids such as isopropyl 5-[4-bromo-1-methyl-5-(trifluoromethyl)-1 H-pyrazole-3-yl]-2-chloro-4-fluorobenzoate. While the invention is preferably directed to the preparation of such 3-aryl-5-haloalkyl-pyrazoles, the invention also relates to the individual process steps for forming phenyl-diketones, forming and alkylating pyrazoles, brominating pyrazoles and other heterocyclic compounds, oxidizing alkyl-substituted benzene compounds, and esterifying carboxylic acids.
Various substituted aryl-pyrazole compounds are known and used as chemical intermediates, pharmaceuticals and herbicides. Exemplary U.S. Pat. Nos. 3,326,662 to Tomoyoshi et al., 3,948,937 to Johnson et al., 4,008,249 to Fischer, deceased et al., 4,072,498 to Moon et al., 4,260,775 to Plath et al., 4,468,871 to Ebel et al., 4,752,326 to Ohyama et al., 5,032,165 to Miura et al., 5,045,106 to Moedritzer et al. A variety of 3-aryl-5-haloalkyl pyrazoles are disclosed in U.S. Pat. Nos. 5,281,571 and 5,489,571 to Woodard et al.
Processes are generally known for making aryl-pyrazole compounds. U.S. Pat. No. 5,281,571 to Woodard et al. sets forth a method for preparing substituted 3-aryl-5-haloalkyl-pyrazoles. Briefly, an acetophenone having a methyl substituent on the phenyl moiety is reacted with an ester in the presence of a base to form a phenyl diketone, which is subsequently isolated and then cyclized by treatment with hydrazine. The resulting aryl-pyrazole is subjected to further process steps, including N-alkylation and halogenation of the pyrazole moiety, oxidation of the methyl group on the phenyl moiety to form a benzoic acid, and formation of benzoic acid derivatives thereof.
While methods such as these are suitable for preparing substituted 3-aryl-5-haloalkyl-pyrazoles, the methods are not optimized with regard to minimizing the expense of reagents, maximizing the selectivity of regioisomers, or maximizing product yields and throughput.